Here's a case where auto completion is exactly what I want, but it's behaving
erratically. Spreadsheet is a work schedule for my wife's staff at work.

I have 12 columns (two per day M-F, one per day S&S). The rows are hours of
the day. Right above where the names go, I added hidden rows with the 5
possible names in each column. The idea of course is you only have to enter
sometimes one letter (sometimes more) and the match will come up and save a
lot of typing. But it works erratically, some cells work many don't. Which
are already filled in seems to affect it, but not very predictably. Some of
the columns are identical, so what works in one should work in the others.
I've checked spelling and formatting and cannot come up with an explanation.
Docs don't explain within how many cells the examples must be.

I'd rather not use the list selection or validation methods -
auto-completion is easier imo (when it works).

Forgot to say Excel 2003, XP HE SP2.